The present invention relates to sprockets for use in conveyor belt and conveyor chain systems and, more particularly, to relatively inexpensive and easily made plastic body sprockets which have replaceable plastic and/or metal teeth so as to enable quick, simple and generally low cost repair to be effected in the commercial/industrial environment when sprocket tooth failure occurs in a conveyor belt or chain installation.
Conveyor belts and chains used in industrial and commercial installations commonly are made of metal or plastic or ceramics. Manufacturers of these belts and chains usually specify that drive sprockets for effecting belt/chain advance be provided at drive locations in numbers of one sprocket per 6 inches of conveyor width so that both adequate conveyor support and drive transmission of the conveyor be achieved. With belt widths most often being three, four or more feet, and with use of sprockets at both ends of a conveyor course, presence of large numbers of sprockets in conveyors is the rule. Totals of 20 or 30 sprockets per conveyor are not unusual.
In recognition that sprocket failure in systems having many sprockets can involve unusually heavy replacement costs, industry generally follows the practice of making sprockets from cheap materials such as plastics or cast iron. The sprockets are made as one-piece components with the view that same are to be discarded when a break therein such as loss of a tooth occurs or, wear renders the sprocket unfit for further use.
It also is known that heavy drive loadings, abrasion, high speed and other factors work effect on sprockets, especially in the food and pharmaceutical industries, which mandate replacement even though no break or wear condition exists since continued use of a given sprocket can produce contamination potentials which cannot be allowed to exist in food/pharmaceutical production lines.
Replacement of sprockets in some instances becomes an almost continuous routine. In many installations access to sprockets is burdensome particularly in respect of having to remove undamaged sprockets from a common drive shaft to get at a damaged one. Actual replacement material and labor costs while not to be minimized are frequently a small cost in comparison to "downtime" losses experienced when a busy and profitable production line must be stopped for a lengthy time to allow sprocket replacement to be effected.
Use of replaceable teeth sprockets in effort to mitigate some of the disadvantages enumerated above is known in the prior art. Instances of and types of replaceable teeth sprockets of which applicants are aware, are for use with metal constructed sprockets and as represented, e.g., by the teachings of U.S. Pat. Nos. 2,038,695; 3,996,814; 3,381,354; 4,308,019; 4,522,611; 4,708,698 and 4,752,281. The devices disclosed in these patents have in common, the use of replaceable teeth or tooth-like elements on a mounting body or hub with mechanical fasteners, these fasteners comprising multiple pieces and in most cases involving some extensive work and piece manipulations to make a replacement.
U.S. Pat. Nos. 655,943 and 3,069,922 also disclose mechanical fastening of replaceable teeth, and while in some ways a little less complicated than the first herein listed group of patents, involve in use labor and costs avoidable if a replacement tooth was simply insertable in place on a wheel or hub without fasteners. U.S. Pat. No. 3,069,993 which discloses insertion of tapered surfaced metal teeth in companion tapered peripheral recesses of a metal cylindrical hub has the added disadvantage of employing small included angle recess defining structure on the hub resulting in inherently weak intersecting surfaces in the recess defining structure promotive of failure during service.
Use of replaceable tooth sprockets employing special fasteners as noted, have the drawbacks of taking unusual time to make replacement, can involve high cost for fasteners, special machining etc. Use of fastener components allows that they can in instances work loose and enter a production line operation. Where sterile and sanitary requirements must be maintained in a system, loose machine parts can contaminate the system. Contamination of a system aside from any repair downtime presents the requirement of reestablishing sterile conditions.